1. Field of the Invention
The present invention relates to an optical pick-up for reproducing data recorded on a recording surface of a disc, or recording data thereon, and a disc unit using thereof.
2. Description of the Related Art
An optical pick-up used in general is mainly composed of three blocks, that is, an objective lens drive device, an optical system and a flexible printed board. The objective lens drive device drives an objective lens in a focusing direction and a tracking direction so as to follow the rotation of an optical disc in order to precisely record or reproduce data. The optical system is composed of an optical component for converging a laser beam by means of the objective lens so as to reproduce data on the disc with the use of a reflected beam, or concentrating the energy of the laser beam onto a recording layer of the disc so as to record date thereon. The flexible printed board connects the lens drive device and the optical system, electrically to an external circuit board.
The above-mentioned optical pick-up is incorporated therein, as main heat generating components, a semiconductor laser for emitting a laser beam, a laser driver IC for controlling the drive of the semiconductor laser, a front monitor for monitoring a laser power upon recording, a photo detector for detecting a reflection beam from a disc and a coil for driving the objective lens in the focusing direction and the tracking direction. Due to heat generation from these components, the temperature of the optical pick-up is raised. In particular, with a writable optical pick-up capable of recording data on a disk such as DVD-RAM/R/RW, CD-R/RW or the like, the heat generation from the semiconductor laser and the laser driver IC is larger. Further, the higher the recording speed, the higher the power of the semiconductor laser is required. Further, in order to ensure the transmission characteristic, it is required to locate the semiconductor laser and the laser driver IC adjacent to each other. In particular, in the case of a DVD recording speed not less than 8×, a circuit, the so-called write strategy, for creating a recording signal waveform has to be incorporated in the laser drive IC in order to transmit a satisfactory high frequency signal to the semiconductor laser. This circuit which has been conventionally incorporated in an IC in a circuit board on the optical disc unit side, causes the heat generation of the laser driver IC to be further increased. Thus, there would be caused deterioration of its performance, lowering of its service life and malfunctioning and the like.
In order to solve the above-mentioned problem of heat generation, there has be presented an optical pick-up in which a heat spreader for the laser driver IC is connected by soldering to a copper foil pattern on a mounting surface of the laser driver IC provided on the flexible printed board and connected to a copper foil on the rear surface through a through hole, and the copper foil on the rear surface thereof is connected to a pick-up cover made of a copper alloy (Refer to an example shown in FIG. 10, which is an application of “Perfect Manual of Thermal Design for Electronics” Nikkan Kogyo Shinbun Co. Jul. 18, 1997 by Naoki Kunimine, Vo., p 130 to 131 and FIG. 11-11). With this configuration, a heat generated from the laser driver IC is dissipated over a sufficiently wide area by the copper foil on the rear surface and the pick-up cover, and accordingly, it is said that the temperature of the laser driver IC can be restrained to a low value.
The above-mentioned conventional technology has caused such a problem that a sufficiently wide area of the copper foil pattern for a wiring patter by which the laser driver IC is mounted, has not been able to be ensured since the copper foil pattern is used for mounting the laser driver IC if the flexible printed board has a single copper foil layer. Further, in the case of using a stainless group metal having a low heat conductivity for the pick-up cover, a heat from the laser driver IC cannot be dissipated in-planewise, and accordingly, sufficient heat radiation cannot be expected.